There are many applications that require measurement of the quantity of oil that is present in a liquid. For example, in pipes leading from oil production or refining facilities it may be required to measure the amount of oil that is present in the liquid (mainly water) flowing in the pipes. To this end it is known to provide an in-line measurement apparatus which measures the amount of oil that is present.
Oil has a natural fluorescence and so, commonly, such measurement apparatus measure the quantity of oil by the detection of fluorescence. Apparatus that detect and/or measure fluorescence are commonly referred to as fluorometers. A fluorometer usually includes a light source for causing fluorescence in a target substance and a detector for measuring the resultant fluorescence.
A typical in-line fluorometer has a measurement window through which the excitation light source is transmitted into a measurement region and through which the resultant fluorescent light is received by the fluorometer. One problem with such fluorometers is the fouling of the measurement window by substances within the measurement region. This problem may be addressed by using an ultrasonic device to clean the window. The ultrasonic device may also be used to agitate the liquid/oil under measurement and this helps to create, by emulsification and homogenisation, a consistent particle or droplet size for the suspended oil which in turn facilitates consistent measurement of fluorescence.
Conventional in-line fluorometers suffer from a variety of problems that impair their performance, including poor efficiency resulting from losses in the optical circuit, and the turbidity of liquid being measured.
It would be desirable, therefore, to provide an improved apparatus for measuring fluorescent material in a liquid.